Sketch items from around the house. Short 30 minutes or less contour line drawing.
Do some longer studies using shading to add dimension and depth
Sketch larger objects, focusing on proportion.
Go out in the fresh air and sketch some trees. Experiment with different media.
Food is another excellent source for sketching. Who knew macaroni and cheerios could be so interesting!? Experiment with different media, pencil, acrylic, colored pencil.
Quick 30 second or one minute gesture drawings are excellent exercises in observation and drawing. I did these during my son's gymnastics class.
Another classic subject matter is the portrait of others and yourself.
Always remember, Practice makes perfect. And Patience, Patience, Patience.